2.2.0.7 false Condensed Consolidated Balance Sheets (Unaudited) (USD $) 0130 - Statement - Condensed Consolidated Balance Sheets (Unaudited) true false In Thousands false false 1 USD false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 2 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ 4 Current Assets: 2 us-gaap_AssetsCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 5 Cash and cash equivalents 3 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 266278000 266278 false false false 2 true true false false 689722000 689722 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 6 Restricted cash and cash equivalents 3 us-gaap_RestrictedCashAndInvestmentsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 31743000 31743 false false false 2 false true false false 43135000 43135 false false false xbrli:monetaryItemType monetary The current cash, cash equivalents and investments that are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes current cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 7 Receivables -- 3 us-gaap_ReceivablesNetCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 8 Customer accounts receivable 4 us-gaap_AccountsReceivableGrossCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1180856000 1180856 false false false 2 false true false false 953222000 953222 false false false xbrli:monetaryItemType monetary Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Subparagraph a, b -Article 5 false 9 Unbilled revenues 4 so_UnbilledRevenuesCurrent so false debit instant Carrying amount at the balance sheet date of revenues which have been earned but not yet billed. false false false false false false false false false false false verboselabel false 1 false true false false 496265000 496265 false false false 2 false true false false 394492000 394492 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of revenues which have been earned but not yet billed. No authoritative reference available. false 10 Under recovered regulatory clause revenues 4 so_UnderRecoveredRegulatoryClauseRevenues so false debit instant Carrying amount at the balance sheet date of customer accounts receivable for retail and wholesale under recovered fuel... false false false false false false false false false false false verboselabel false 1 false true false false 193998000 193998 false false false 2 false true false false 333459000 333459 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of customer accounts receivable for retail and wholesale under recovered fuel costs, and other under recovered regulatory costs. No authoritative reference available. false 11 Other accounts and notes receivable 4 so_OtherAccountsNotesAndLoansReceivable so false debit instant Amounts due from customers or clients, within one year of the balance sheet date (or one operating cycle, if longer), for... false false false false false false false false false false false verboselabel false 1 false true false false 352798000 352798 false false false 2 false true false false 374670000 374670 false false false xbrli:monetaryItemType monetary Amounts due from customers or clients, within one year of the balance sheet date (or one operating cycle, if longer), for goods or services that have been delivered or sold in the normal course of business and an amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date within one year of the balance sheet, not elsewhere specified in the taxonomy. No authoritative reference available. false 12 Accumulated provision for uncollectible accounts 4 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -27152000 -27152 false false false 2 false true false false -24568000 -24568 false false false xbrli:monetaryItemType monetary A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 false 13 Fossil fuel stock, at average cost 3 us-gaap_EnergyRelatedInventoryOtherFossilFuel us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1383220000 1383220 false false false 2 false true false false 1446984000 1446984 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of other types of fuel derived from living matter of a previous geologic time, not otherwise itemized. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 false 14 Materials and supplies, at average cost 3 us-gaap_OtherInventorySupplies us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 805205000 805205 false false false 2 false true false false 793847000 793847 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 4 -Paragraph 3 false 15 Vacation pay 3 so_VacationPay so false debit instant Carrying amount at the balance sheet date of the regulatory asset related to vacation pay to employees. false false false false false false false false false false false verboselabel false 1 false true false false 145422000 145422 false false false 2 false true false false 145049000 145049 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of the regulatory asset related to vacation pay to employees. No authoritative reference available. false 16 Prepaid expenses 3 us-gaap_PrepaidExpenseCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 479878000 479878 false false false 2 false true false false 508338000 508338 false false false xbrli:monetaryItemType monetary Sum of the amounts paid in advance for capitalized costs that will be expensed with the passage of time or the occurrence of a triggering event, and will be charged against earnings within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 false 17 Other regulatory assets, current 3 so_OtherRegulatoryAssetsCurrent so false debit instant Carrying amount of other regulatory assets (not elsewhere included) as of the balance sheet date of capitalized costs of... false false false false false false false false false false false verboselabel false 1 false true false false 175237000 175237 false false false 2 false true false false 166549000 166549 false false false xbrli:monetaryItemType monetary Carrying amount of other regulatory assets (not elsewhere included) as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. No authoritative reference available. false 18 Other current assets 3 us-gaap_OtherAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 40514000 40514 false false false 2 false true false false 48558000 48558 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of current assets not separately presented elsewhere in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 true 19 Total current assets 3 us-gaap_AssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 5524262000 5524262 false false false 2 false true false false 5873457000 5873457 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 9 -Article 5 true 20 Property, Plant, and Equipment: 2 us-gaap_PropertyPlantAndEquipmentNetAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 21 In service 3 us-gaap_PropertyPlantAndEquipmentGross us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 55698851000 55698851 false false false 2 false true false false 53587853000 53587853 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, physical structures, machinery, vehicles, furniture, computer equipment, construction in progress, and similar items. Amount does not include depreciation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 false 22 Less accumulated depreciation 3 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 19647708000 19647708 false false false 2 false true false false 19121271000 19121271 false false false xbrli:monetaryItemType monetary The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -Subparagraph c Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 14 -Article 5 true 23 Plant in service, net of depreciation 3 so_PlantInServiceNetOfDepreciation so false debit instant Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not... false false false false false false false false false false false verboselabel false 1 false true false false 36051143000 36051143 false false false 2 false true false false 34466582000 34466582 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not intended for resale, less depreciation. No authoritative reference available. false 24 Nuclear fuel, at amortized cost 3 so_NuclearFuelAtAmortizedCost so false debit instant The carrying amount as of the balance sheet of nuclear fuel held as property plant and equipment. This amount is net of... false false false false false false false false false false false verboselabel false 1 false true false false 677178000 677178 false false false 2 false true false false 593119000 593119 false false false xbrli:monetaryItemType monetary The carrying amount as of the balance sheet of nuclear fuel held as property plant and equipment. This amount is net of amortization based on the energy produced over the life of the fuel. No authoritative reference available. false 25 Construction work in progress 3 us-gaap_ConstructionInProgressGross us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3902173000 3902173 false false false 2 false true false false 4170596000 4170596 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of long-lived asset under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 true 26 Total property, plant, and equipment 3 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 40630494000 40630494 false false false 2 false true false false 39230297000 39230297 false false false xbrli:monetaryItemType monetary Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, and production equipment. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 13 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 12 -Paragraph 5 -Subparagraph b, c Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 8 -Article 7 true 27 Other Property and Investments: 2 us-gaap_LongTermInvestmentsAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 28 Nuclear decommissioning trusts, at fair value 3 us-gaap_DecommissioningFundInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1055036000 1055036 false false false 2 false true false false 1070117000 1070117 false false false xbrli:monetaryItemType monetary Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 false 29 Leveraged leases 3 us-gaap_LeveragedLeasesBalanceSheetInvestmentInLeveragedLeasesNet us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 614830000 614830 false false false 2 false true false false 610252000 610252 false false false xbrli:monetaryItemType monetary Rentals receivable and estimated residual value of leased assets less principal and interest on nonrecourse debt, unearned income, and deferred taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 47 false 30 Miscellaneous property and investments 3 us-gaap_OtherLongTermInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 286142000 286142 false false false 2 false true false false 282974000 282974 false false false xbrli:monetaryItemType monetary Other noncurrent investments not otherwise specified in the taxonomy, not including investments in marketable securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph f -Article 7 true 31 Total other property and investments 3 us-gaap_LongTermInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 1956008000 1956008 false false false 2 false true false false 1963343000 1963343 false false false xbrli:monetaryItemType monetary The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle). No authoritative reference available. true 32 Deferred Charges and Other Assets: 2 so_DeferredChargesAndOtherAssetsAbstract so false na duration Deferred Charges and Other Assets. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Deferred Charges and Other Assets. false 33 Deferred charges related to income taxes 3 so_DeferredChargesRelatedToIncomeTaxes so false debit instant Noncurrent regulatory assets associated with deferred income tax liabilities that are expected to be recovered from customers... false false false false false false false false false false false verboselabel false 1 false true false false 1167278000 1167278 false false false 2 false true false false 1047452000 1047452 false false false xbrli:monetaryItemType monetary Noncurrent regulatory assets associated with deferred income tax liabilities that are expected to be recovered from customers through the ratemaking process. No authoritative reference available. false 34 Unamortized debt issuance expense 3 us-gaap_UnamortizedDebtIssuanceExpense us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 199558000 199558 false false false 2 false true false false 208346000 208346 false false false xbrli:monetaryItemType monetary The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. No authoritative reference available. false 35 Unamortized loss on reacquired debt 3 us-gaap_UnamortizedLossReacquiredDebtNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 255180000 255180 false false false 2 false true false false 254936000 254936 false false false xbrli:monetaryItemType monetary Unamortized Loss on Reacquired Debt is the loss incurred upon reacquisition or refinancing of debt, is treated as a deferred charge and amortized over the life of the new debt issued. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9 false 36 Deferred under recovered regulatory clause revenues 3 so_DeferredUnderRecoveredRegulatoryClauseRevenues so false debit instant Carrying amount at the balance sheet date of underrecovered fuel costs allowed to be deferred by regulatory authorities, that... false false false false false false false false false false false verboselabel false 1 false true false false 479896000 479896 false false false 2 false true false false 373245000 373245 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of underrecovered fuel costs allowed to be deferred by regulatory authorities, that are expected to be recoverable through rate adjustments after one year. No authoritative reference available. false 37 Other regulatory assets, deferred 3 so_OtherRegulatoryAssetsDeferred so false debit instant Carrying amount of other regulatory assets (not elsewhere identified) as of the balance sheet date of capitalized costs of... false false false false false false false false false false false verboselabel false 1 false true false false 2724931000 2724931 false false false 2 false true false false 2701910000 2701910 false false false xbrli:monetaryItemType monetary Carrying amount of other regulatory assets (not elsewhere identified) as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. No authoritative reference available. false 38 Other deferred charges and assets 3 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 436883000 436883 false false false 2 false true false false 392880000 392880 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of noncurrent assets not separately disclosed in the balance sheet due to materiality considerations. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 true 39 Total deferred charges and other assets 3 so_TotalDeferredChargesAndOtherAssets so false debit instant Sum of the carrying amounts as of the balance sheet date of all assets, excluding Property, Plant, and Equipment and Other... false false false false false false false false false false false totallabel false 1 false true false false 5263726000 5263726 false false false 2 false true false false 4978769000 4978769 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets, excluding Property, Plant, and Equipment and Other Property and Investments, that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer. No authoritative reference available. true 40 Total Assets 2 us-gaap_Assets us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 53374490000 53374490 false false false 2 false true false false 52045866000 52045866 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Concepts (CON) -Number 6 -Paragraph 25 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 18 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7 true 42 Current Liabilities: 2 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 43 Securities due within one year 3 us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1514465000 1514465 false false false 2 false true false false 1112705000 1112705 false false false xbrli:monetaryItemType monetary Obligation related to long-term debt (excluding convertible debt) and capital leases, the portion which is due in one year or less in the future. No authoritative reference available. false 44 Notes payable 3 us-gaap_ShortTermBorrowings us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 881638000 881638 false false false 2 false true false false 639199000 639199 false false false xbrli:monetaryItemType monetary Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph 2, 3 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Subparagraph a(1) -Article 7 false 45 Accounts payable 3 us-gaap_AccountsPayableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1282523000 1282523 false false false 2 false true false false 1329448000 1329448 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a -Article 5 false 46 Customer deposits 3 us-gaap_CustomerDepositsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 335625000 335625 false false false 2 false true false false 330582000 330582 false false false xbrli:monetaryItemType monetary The current portion, due within one year or the normal operating cycle, if longer, of money or property received from customers which is either to be returned upon satisfactory contract completion or applied to customer receivables in accordance with the terms of the contract or the understandings. No authoritative reference available. false 47 Accrued taxes - 3 us-gaap_TaxesPayableCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 48 Accrued income taxes 4 us-gaap_AccruedIncomeTaxesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 25664000 25664 false false false 2 false true false false 13005000 13005 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all currently due domestic and foreign income tax obligations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph b(1) -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 15, 21 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Section Appendix E -Paragraph 289 false 49 Unrecognized tax benefits 4 so_UnrecognizedTaxBenefitsAccruedTaxes so false credit instant Liability associated with tax benefits that do not currently fully meet the "more likely than not" threshold as defined by... false false false false false false false false false false false verboselabel false 1 false true false false 168400000 168400 false false false 2 false true false false 165645000 165645 false false false xbrli:monetaryItemType monetary Liability associated with tax benefits that do not currently fully meet the "more likely than not" threshold as defined by FIN 48. This line item includes both federal and state taxes. No authoritative reference available. false 50 Other accrued taxes 4 us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 319321000 319321 false false false 2 false true false false 398384000 398384 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 10 -Section A -Paragraph 16 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 51 Accrued interest 3 us-gaap_InterestPayableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 220153000 220153 false false false 2 false true false false 218188000 218188 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 52 Accrued vacation pay 3 us-gaap_AccruedVacationCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 181150000 181150 false false false 2 false true false false 183911000 183911 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred and payable for unused vacation time owed to employees based on the entity's vacation benefit given to its employees. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 8 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 43 -Paragraph 13 false 53 Accrued compensation 3 us-gaap_AccruedSalariesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 222301000 222301 false false false 2 false true false false 247950000 247950 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of the obligations incurred through that date and payable for employees' services provided. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7, 8 false 54 Liabilities from risk management activities 3 us-gaap_DerivativeInstrumentsAndHedgesLiabilities us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 124154000 124154 false false false 2 false true false false 124648000 124648 false false false xbrli:monetaryItemType monetary Sum as of the balance sheet date of the (a) fair values of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and (b) the carrying amounts of the liabilities arising from financial instruments or contracts used to mitigate a specified risk (hedge), and which are expected to be extinguished or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements. No authoritative reference available. false 55 Other regulatory liabilities, current 3 so_OtherRegulatoryLiabilitiesCurrent so false credit instant The amount for other current regulatory liabilities not elsewhere included. Regulatory liabilities represent probable future... false false false false false false false false false false false verboselabel false 1 false true false false 297328000 297328 false false false 2 false true false false 528147000 528147 false false false xbrli:monetaryItemType monetary The amount for other current regulatory liabilities not elsewhere included. Regulatory liabilities represent probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. These revenues are expected to be credited within one year. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 21 -Article 5 true 58 Long-term Debt 2 us-gaap_LongTermDebtAndCapitalLeaseObligations us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 18134554000 18134554 false false false 2 false true false false 18131244000 18131244 false false false xbrli:monetaryItemType monetary Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer plus capital lease obligations due to be paid more than one year after the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section H true 59 Deferred Credits and Other Liabilities: 2 so_DeferredCreditsAndOtherLiabilitiesAbstract so false na duration Deferred Credits and Other Liabilities. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Deferred Credits and Other Liabilities. false 60 Accumulated deferred income taxes 3 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 6725211000 6725211 false false false 2 false true false false 6454822000 6454822 false false false xbrli:monetaryItemType monetary Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise shall separate deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. 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No authoritative reference available. true 70 Redeemable Preferred Stock of Subsidiaries 2 us-gaap_TemporaryEquityCarryingAmount us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 374496000 374496 false false false 2 false true false false 374496000 374496 false false false xbrli:monetaryItemType monetary The carrying value (book value) of an entity's issued and outstanding stock which is not included within permanent equity in Stockholders Equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer. 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